The gross weight of an aircraft will generally decrease as the aircraft burns fuel during flight. The more accurately the changing gross weight of the aircraft can be determined during flight, the more accurately flight parameters or related information such as heading, thrust, altitude, airspeed, descent rate, and time of arrival can be determined for a given flight plan to increase fuel efficiency and/or reduce the release of carbon dioxide into the atmosphere.
Existing methods for determining the gross weight of an aircraft during flight include subtracting the weight of fuel that has been burned during flight from the known initial gross weight of the aircraft (e.g., the aircraft's “zero fuel weight” plus the weight of the fuel initially onboard the aircraft). One way of determining the amount of fuel burned during flight is to monitor the amount of unburned fuel that remains in the fuel tank with a float sensor. However, float sensors can be unreliable if the aircraft is not engaged in level flight or for other reasons. Another way of determining the amount of fuel burned during flight is to monitor the amount of fuel that flows from the tank to the engines. Many aircraft have multiple fuel tanks and, as a result, the fuel remaining in each tank or the fuel that flows out of each tank must be monitored and is subject to measurement error. For either of the methods described above, these errors can compound significantly, especially over long flights. Both methods also rely on knowledge of the aircraft's zero fuel weight, the initial fuel weight, and/or the initial gross weight of the aircraft, and difficulties arise if that information is difficult to obtain. This creates a need for systems and methods for in-flight aircraft gross weight determination that are not dependent on knowledge of the zero fuel weight of the aircraft and/or the weight of its initial load of fuel, and that are not dependent on determining the fuel remaining in the tank or the fuel that has been burned during flight.